Sharing Variables

BUILD files are intended to be simple and declarative. They will typically
consist of a series of a target declarations. As your code base and your BUILD
files are getting larger, you will probably notice some duplication, e.g.

Code duplication in BUILD files is usually fine. This can make the file more
readable: each declaration can be read and understood without any context. This
is important, not only for humans, but also for external tools. For example, a
tool might be able to read and update BUILD files to add missing dependencies.
Code refactoring and code reuse might prevent this kind of automated
modification.

With that in mind, it is possible to share values, if you still believe it would
be useful (e.g. values must be kept in sync). We can update the previous example
and introduce a variable: